Systems and methods for catheter tip placement using ECG

ABSTRACT

A system and method for catheter placement using ECG is provided. In certain embodiments, the system and method can generate a patient specific window for tracking a characteristic of an ECG waveform, such as the amplitude of a P-wave. The patient specific window can be utilized in a system and method for assisting in the placement of a catheter within a patient. In other embodiments, a tip location algorithm can be used with an anti-thrombogenic catheter and an intravascular electrode assembly for maintaining a high resolution intravascular signal in an ECG based catheter tip placement system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/782,913, filed on Mar. 14, 2013 and titled Method for Locating aCatheter Using Intracardial ECG, incorporated herein by reference intheir entireties.

FIELD OF THE INVENTION

The present invention relates generally to positioning a catheter tipwithin a human body. More specifically, the invention relates to systemsand methods that utilize ECG for assisting with catheter tip placementprocedures.

BACKGROUND OF THE INVENTION

Medical professionals commonly use catheters for gaining prolongedaccess to an area within the body. Once the catheter tip is positionedat the target location, treatments such as antibiotics, chemotherapy,pain medicine, and nutrition can be administered. If the catheter tip isimproperly positioned during insertion, various risks to the patientarise, including a fluid infusion that causes pain or injury to thepatient, complications due to increased thrombosis rates, delays intherapy, catheter malfunction and additional costs.

General standards for proper catheter insertion depend on the type ofcatheter and the treatment being provided. For example, peripherallyinserted central catheters (or PICC lines) are commonly inserted into abrachial, cephalic or basilic vein in the arm and advanced through thevenous system towards the superior vena cava (SVC). Current medicalstandards recommend that the distal tip of the catheter terminate in thelower ⅓ of the SVC, close to the junction of the SVC and the rightatrium (RA). However, since PICCs are commonly inserted into a vein inthe arm and advanced through the venous system to reach the SVC, thePICC line tip may be inadvertently positioned in a non-target area, suchas the internal jugular, the subclavian vein, or too far past the SVC-RAjunction and into the heart.

Catheter tip location techniques have improved the ability of medicalprofessionals to verify the location of the catheter tip. One techniqueuses fluoroscopy to confirm tip location. Fluoroscopy provides theoperator with real-time images of the patient's anatomy using afluoroscope. Another technique uses a combination of an electromagneticbeacon and an electromagnetic detection element to track the beaconpositioned near the catheter tip. Many techniques have also beendescribed for using electrocardiography (ECG) to assist with cathetertip placement by measuring an ECG signal from an intravascular (IV)electrode positioned at or near the catheter tip.

Tracking ECG waveform changes measured from an IV electrode as thecatheter advances through the vasculature towards the SA node canprovide valuable feedback to the medical professional placing thecatheter, since the SA node is located near the SVC-RA junction.Specifically, tracking the P-wave morphology is known to be a valuabletool. For example, as the IV electrode advances down the SVC towards theSA node, the amplitude of the P-wave will start to rise. The amplitudeof the P-wave will eventually peak when the IV electrode is closest tothe SA node, and eventually start to decrease in amplitude as the IVelectrode moves away from the SA node and enters the RA. Observation ofthis phenomenon has been utilized by medical professionals for catheterplacement procedures at least as early as the mid-20th century.

Automated systems that track P-wave morphology for catheter tipplacement have also been previously described. For example, in U.S. Pat.No. 5,121,750 to Katims, incorporated herein by reference, a monitoringsystem detects changes in the P-wave as measured from an IV electrodefor providing automated user instructions on catheter placement. Themonitoring system (1) detects increases in the P-wave amplitude as theIV electrode approaches the SA node and signals the user to continueadvancing the catheter, (2) detects a decrease in the P-wave amplitudeas the IV electrode passes the SA node and signals the user to pull backthe catheter, and (3) detects that the P-wave is within a certain rangeof the maximum and signals the user to stop once within that range.

For tip positioning systems that rely on tracking changes in P-waveamplitude for providing user feedback, several obstacles may arise. Forinstance, P-wave location and morphology can change from patient topatient based on a number of factors (explained in further detailbelow). It would be beneficial for an ECG and P-wave based tip locationsystem to have a more patient specific analysis approach to account forpatient-to-patient variability. Further, ECG signals from IV electrodestend to have low resolution due to a number of factors, includingelectrode downsizing and design limitations, movement, and pickup ofphysiologic and extraphysiologic artifacts. A noise spike may cause thealgorithm to misinterpret the acquired signal, possibly leading toerroneous user feedback. Systems that can accurately provide userfeedback, manage lower resolution IV electrode signals, and minimize theinfluence of ECG artifacts on signal processing would be advantageous.

Further, problems such as thrombus buildup at the catheter tip andwithin the catheter lumen can affect IV ECG signal acquisition. Thrombusbuildup can partially block electrode exposure which can result in amuted signal. Further, thrombus buildup in contact or near the electrodecan cause the IV ECG signal to refract off of the thrombus formations,adding noise to the IV ECG waveform. To clear the catheter lumen andopening of thrombus, and to combat the formation of new thrombus, thecatheter lumen can be flushed with saline. However, this can add timeand cost to the procedure. Further, prolonged interruptions in catheteradvancement may interfere with the normal execution of the tip locationalgorithm, and may prevent the algorithm from properly executing, orlead to erroneous user feedback.

Improved catheter tip placement systems and methods for overcoming theseissues is desired.

SUMMARY OF THE INVENTION

The invention is directed to a system and method for catheter tipplacement using ECG. In one aspect, the invention is a system and methodfor establishing an ECG search window for catheter tip placement. Inanother aspect, the invention is a system and method for assisting inthe placement of a catheter within a patient. In yet another aspect, theinvention is a system and method for high clarity signal acquisition intip location systems utilizing an intravascular electrode. In certainaspects, a method for establishing an ECG search window for a cathetertip placement system includes the steps of acquiring multiple surfaceECG signals from at least one surface ECG electrode; generating a signalaveraged surface ECG signal from the multiple surface ECG signals;determining a first fiducial point by identifying an extremum within thesignal averaged surface ECG signal; establishing a first ECG searchwindow between first and second predetermined values offset from thefirst fiducial point; determining a second fiducial point by identifyingan extremum in the first ECG search window; determining a search windowbeginning value by identifying a local extremum on a first side of thesecond fiducial point, and determining a search window ending value byidentifying a local extremum on a second side of the second fiducialpoint; and establishing a second ECG search window between the searchwindow beginning value and the search window ending value so that thesecond ECG search window is narrower than the first ECG search window.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing purposes and features, as well as other purposes andfeatures, will become apparent with reference to the description andaccompanying figures below, which are included to provide anunderstanding of the invention and constitute a part of thespecification, in which like numerals represent like elements, and inwhich:

FIG. 1 is a diagram of an upper portion of a human body illustratingvarious positions of the vasculature, including the SVC, RA and SA node;

FIG. 2 is an exemplary ECG waveform showing typical shapes and positionsof common ECG waves;

FIGS. 3A-3F are exemplary P-wave morphologies; FIG. 3A shows a normalP-wave; FIG. 3B shows a P-wave with a higher initial positivedeflection; FIG. 3C shows a P-wave with a notch near the peak; FIG. 3Dshows a prolonged P-wave; FIG. 3E shows an offset P-wave; FIG. 3F showsa spike artifact followed by a normal P-wave;

FIGS. 4A-4C are diagrams of a human body illustrating various surfaceelectrode configurations according to exemplary embodiments of theinvention; FIG. 4A illustrates a 3 surface electrode configuration; FIG.4B illustrates a 4 surface electrode configuration; FIG. 4C illustratesa 3 surface electrode configuration with an IV electrode;

FIG. 5 is a diagram of a catheter tip placement system according to anexemplary embodiment of the invention;

FIG. 6 is a set of waveforms diagram showing a search window generatedaccording to a surface ECG waveform and overlaid onto an IV ECG waveformaccording to an exemplary embodiment of the invention;

FIGS. 7A and 7B show a flow chart for a tip location algorithm accordingto an exemplary embodiment of the invention;

FIGS. 8A-8D show a tip location user feedback graphical user interface(GUI) according to an exemplary embodiment of the invention; FIG. 8A isa graphical view of a GUI command to move forward; FIG. 8B is agraphical view of a GUI command to move backward; FIG. 8C is a graphicalview of a level indicator GUI command to stop; and FIG. 8D is agraphical view of a GUI including user commands, IV ECG waveforms andsurface ECG waveforms;

FIG. 9A is a perspective view of a conventional catheter coaxiallysurrounding a stylet.

DETAILED DESCRIPTION OF THE INVENTION

The present invention can be understood more readily by reference to thefollowing detailed description, the examples included therein, and tothe Figures and their following description. The drawings, which are notnecessarily to scale, depict selected preferred embodiments and are notintended to limit the scope of the invention. The detailed descriptionillustrates by way of example, not by way of limitation, the principlesof the invention. The skilled artisan will readily appreciate that thedevices and methods described herein are merely examples and thatvariations can be made without departing from the spirit and scope ofthe invention. It is also to be understood that the terminology usedherein is for the purpose of describing particular embodiments only andis not intended to be limiting. Systems and methods described below arecompatible with ECG assisted placement for a variety of medical devices,including for example PICCs, central venous catheters, midlinecatheters, port catheters, and dialysis catheters.

Referring now in detail to the drawings, in which like referencenumerals indicate like parts or elements throughout the several views,in various embodiments, presented herein are systems and methods forcatheter tip placement using ECG.

As described above, catheters such as PICC lines are commonly insertedinto a brachial, cephalic or basilic vein in the arm and advancedthrough the venous system towards the SVC-RA junction with the goal ofhaving the catheter tip terminate in the lower ⅓ of the SVC. As shown inFIG. 1, a human body 10 has a vasculature system 18 leading to the heart12. Using P-waves as a guidance measure and the SA node (SA) as areference point, an IV electrode located near a PICC tip can trackchanges in the P-wave generated from the SA node (SA) as the PICC tipand IV electrode advance towards the SVC 14 and the RA 16. As describedin Katims, an algorithm can be employed to detect increases in P-waveamplitude as the IV electrode advances from positions A to B, and then Bto C. When the IV electrode passes the SA node (SA) and moves fromposition C to D, the algorithm detects a decrease in P-wave amplitudeand a user command can be given indicating that the PICC be pulled backuntil either the maximum P-wave is reached again, or until a percentageof the maximum P-wave is detected. If, for example, the algorithmdetects a severe and premature drop in P-wave amplitude duringinsertion, or if the P-wave never meets an incrementing threshold, thatcould indicate that the PICC tip accidently migrated up to the internaljugular 20 instead of down towards the SVC 14.

For tip location systems that rely on an algorithm to interpret changesin P-waves, the ability of the system to accurately identify the P-wavegiven patient-to-patient P-wave variability and noise are important tosystem reliability and accuracy. As shown in FIG. 2, the P-wave is nottypically the most prominent wave in an ECG waveform. The QRS complex istypically the most prominent waveform and is therefore considered thesimplest to detect, primarily because of the sharp delineation of theR-wave. Other waves, such as the T-wave or the U-wave (not shown) mayalso present as prominent or diminished depending on various factors.

Patient variability in P-wave morphology is not uncommon. FIGS. 3A-3Fillustrate just a few common examples of P-wave morphologies. A normalP-wave is illustrated in FIG. 3A. A normal P-wave 22 is formed in partby the combination of right and left atrial depolarization waves insequence. The P-wave 23 illustrated in FIG. 3B shows a higher initialpositive deflection, which could be caused by right atrial enlargement,leading to a more pronounced peak during right atrial depolarization.Right atrial enlargement is common in patients suffering from pulmonaryhypertension. Left atrial enlargement could cause a P-wave 24 with anotch near the peak as shown in FIG. 3C, or a prolonged P-wave 25 asshown in FIG. 3D. P mitrale or a notched P-wave may also be due tomitral stenosis. An offset P-wave 26 as shown in FIG. 3E could result inpatients having atrial fibrillation or extrasystoles. Numerous otherfactors including respiratory rate, heart rate, prior surgeries (e.g. aMAZE procedure), or patient conditions (e.g. ventricular tachycardia,Wolff-Parkinson-White syndrome or atrial disease) could impact P-wavemorphology and patient variability.

Even if a patient presents a normal P-wave, an artifact such as thespike artifact shown in the P-wave 27 of FIG. 3F could appear near or ontop of the P-wave, leading to a misinterpretation of the P-waveamplitude during signal processing. In general, artifacts can begenerated from physiologic or extraphysiologic sources, such as patientmovement, electrical noise from other parts of the body, andinterference from medical equipment and other sources of electricaldisturbance in the local environment. Systems and methods according tothe present invention improve P-wave and ECG based tip location systemsas described further below.

According to an embodiment of the invention, multiple surface electrodesand a single IV electrode are utilized for ECG signal acquisition.Alternative embodiments may utilize a single surface electrode ormultiple IV electrodes. In this exemplary embodiment and as illustratedin FIG. 4A, three surface electrodes S1, S2, S3 are placed on a surfaceon the skin of the patient 10 to acquire a surface ECG waveform. Thisconfiguration, utilizes an right arm (RA—white) lead S1, a left arm(LA—black) lead S2, and a left leg (LL—red) lead to form what iscommonly referred to as Einthoven's Triangle. In an alternativeembodiment, an additional neutral lead (N) S4 can be positioned as aright leg lead S4, as shown in FIG. 4B. An IV electrode IV1 will also beutilized by the system for acquiring an IV ECG signal as the IVelectrode is advanced through the vasculature.

As shown in the system diagram of FIG. 5 (and using the exampleconfiguration shown in FIG. 4C), all of the electrodes S1, S2, S3, IV1are operably connected to a central processing unit 30 of the tiplocation system 45. The three surface ECG electrodes S1, S2, S3, and theIV electrode IV1 connect to a signal processing unit 31, where thesignals are acquired and processed by the tip location algorithm. Amemory unit 32 can be used to store data including waveforms, algorithmvariables and error messages. The communication unit 33 on the centralprocessing unit 30 can transmit data via a hardwired or wirelessconnection to a communication unit 43 on a handheld device. The handhelddevice 40 can be for example a smart phone or a table. Alternatively,this device 40 can be a unit mounted on a pole or otherwise stationaryin the medical suite. A display 44 such as a touch-screen display can beintegral to the handheld device, which communicates with thecommunication unit 43 and a memory unit 42. The display can communicateuser feedback to the medical professional performing the procedure, suchas catheter advancement instructions, ECG waveforms and error messages.A touch-screen on the display can be used to communicate informationbetween the medical professional and the tip location system 45. Inalternative embodiments, the central processing unit 30 and the handhelddevice 45 are a single integral unit forming the tip location system 45.

A customized and patient specific IV ECG search window can beestablished under the following method according to an exemplaryembodiment of the invention. For signal acquisition, the patient isprepped with an electrode configuration as illustrated in FIG. 4C. Now,with reference to FIG. 6, a surface ECG waveform 35 is acquired fromsurface ECG electrodes. The surface ECG waveform 35 can represent asingle heartbeat cycle as measured directly from one ECG electrode, awaveform that has been averaged among measurements from multiple surfaceECG electrodes (e.g. Wilson's central terminal), a signal averagedwaveform from one or more surface ECG electrodes averaged over multipleheartbeats, a waveform run through a filter, or a combination of theabove to increase the waveform resolution. In a preferred embodiment,the surface ECG waveform 35 is a signal averaged waveform, averaged frommultiple surface ECG electrodes and further averaged over 10-20heartbeats. Once the signal averaged surface ECG waveform 35 has beengenerated, it is analyzed to find the peak of the R-wave 50 as aninitial fiducial point. A number of R-wave or QRS detection algorithmsknown in the art can be incorporated for this purpose, including PanTomkins, Hilbert transformation, wavelet coefficient estimation, linearfiltering and model based approaches. Alternative fiducial points suchas the onset or offset of the R-wave, the Q-wave or the S-wave can alsobe used.

After the peak of the R-wave 50 is identified, an initial P-wave searchwindow 51 is established based on a generalized area of where the P-wavecan be expected to appear in all patients, accounting for P-wavevariability between patients. In this embodiment, two predeterminedpoints, 220 ms (52) prior to the R-wave peak 50 and 40 ms (53) prior tothe R-wave peak 50 form the beginning and ending of the initial P-wavesearch window 51. Other predetermined points, which may range forexample between 20-60 ms and 200-240 ms can be used. With the initialP-wave search window 51 now established, the peak of the P-wave 54 isidentified as the absolute peak within the initial P-wave search window51. Isolated noise, interference, and aberrant spikes will be filteredout of the surface ECG waveform 35 during the signal averaging step,minimizing the possibility that they will falsely present as theabsolute peak within the initial P-wave search window 51.

Using the peak of the P-wave 54 as a second fiducial point, the firstlocal minima to the left 55 and right 56 sides of the peak of the P-wave54 are identified to form the bounds of a patient specific surface ECGP-wave window 57. A first variable Pb represents the beginning of thesurface ECG P-wave window 57 based on the distance between the minimumto the left side 55 of the peak of the P-wave 54 and the R-wave 50. Asecond variable Pe represents the end of the surface ECG P-wave window57 based on the distance between the minimum to the right side 56 of thepeak of the P-wave 54 and the R-wave 50. In alternative embodiments, itcould be advantageous to expand one or more edges of thepatient-specific P-wave window to a subsequent second or third localminimum. For example, the system might initially identify a notch in theP-wave (see for example FIG. 3C) as the first local minimum (to the leftor right of the P-wave peak). In this case, sensing that the first leftor right local minimum is in too close in proximity (in amplitude ortime) to the P-wave peak, the system may recognize a false edge of theP-wave and expand the window to a subsequent local minimum, generating amore relevant P-wave window for that particular patient. In yet anotheralternative embodiment, edges of the patient specific P-wave window canbe established based on a predetermined distance surrounding the P-wavepeak. Further, patient specific P-wave window edges can be furtherexpanded or narrowed to deal with a number of factors, including P-wavemorphology or noise in signal. Other windows described herein can befurther modified in a similar fashion.

Once the patient specific surface ECG P-wave window 57 is establishedusing the surface ECG waveform 35, it can be overlaid onto the IV ECGwaveform 36 to form a patient specific IV P-wave search window 67. Togenerate the IV P-wave search window 67, the R-wave 60 in the IV ECGwaveform 36 is first identified using a QRS complex or R-wave detectiontechnique. Then, Pb and Pe, determined from analysis of the surface ECG,are offset to the left of the R-wave 60, establishing the beginning 65and ending 66 of the IV P-wave search window 67. This technique allowsthe system to establish a patient specific IV P-wave search window usingthe higher resolution surface ECG waveform, then transfer the surfaceECG P-wave search window to the lower resolution IV ECG signal for moreaccurate signal processing during the catheter placement procedure. If,in this example, a generic non patient specific search window 61 wasapplied to the IV ECG waveform 36 with non patient specific beginning 62and ending 63 points, an artifact spike 69 would have presented as thelocal maximum, throwing off the tip location algorithm which relies ontracking the P-wave amplitude 64. Using this method, the only wave inthe lower resolution IV ECG waveform 36 that needs to be specificallyidentified is the R-wave 60, which is sharply delineated even in lowerresolution ECG waveforms. This improved tip location ECG signalprocessing technique allows for consistent identification of the P-wavein the lower resolution IV ECG waveform, and provides a technique thatis efficient enough to run in real time for live user feedback duringthe catheter placement procedure.

It is important to note that the ECG waveform may appear as inverteddepending on a number of factors affecting waveform polarity, includingfor example ECG lead configuration, whether or not the signalacquisition equipment is set to invert acquired signals, and physicalabnormalities changing normal electrophysiological conduction paths.Thus, for example, if the surface ECG waveform 36 shown in FIG. 6 wasinverted, the R-wave peak 50 and the P-wave peak 54 would present asminimums instead of maximums. The method described above for customizinga patient specific IV ECG search window can be adjusted to detectwaveforms presenting as either local minimums or local maximums sinceeither type of extremum can just as easily be located and tracked.Adjustments for changing the type of extremum being tracked can happenautomatically using a simple test algorithm such as a peak detection orbaseline analysis algorithm. Alternatively, the system can measureabsolute values of extrema so that the displacement of the deflection,and not the positive or negative value of the deflection becomes therelevant measure.

An algorithm for placing a PICC line according to an exemplaryembodiment of the invention is now explained with reference to the flowchart 100 shown in FIGS. 7A and 7B. First, with reference to FIG. 7A, asurface P-wave window is established in similar fashion to the methoddescribed above. ECG signals are acquired from surface ECG electrodes tocreate a signal averaged surface ECG signal 101, and the QRS complex isidentified. The initial window for finding the P-wave is determined bylooking to the left of the R-peak at the period between 40-220 ms priorto the R-wave peak 102. The peak of the P-wave is identified by findingthe absolute maximum of the signal averaged surface ECG in the initialP-wave window. To find a beginning value for a patient specific P-wavewindow, the algorithm first looks at the surface ECG signal left of theP-wave peak and identifies the first local minimum 103. Similarly, tofind an ending value for the patient specific P-wave window, the firstlocal minimum right of the P-wave peak is identified 104. The identifiedleft and right local minimums provide the beginning and ending valuesfor a patient specific window that can now be applied to P-wave analysisin the IV ECG signal as explained above with reference to FIG. 6. A“P-wave threshold” value is also calculated and saved in memory forreference later on in the algorithm (explained in further detail below),and is calculated as the average P-wave amplitude over 10 heartbeatsplus two times the standard deviation 105.

Next, a series of steps for providing user instruction during the PICCplacement procedure are executed based on P-waves acquired from the IVECG electrode located at or near the tip of the PICC. The algorithmbegins to track changes in the P-wave amplitude by looking at theamplitude of the waveform within the patient specific IV P-wave window106. A decision is made based on how the IV ECG P-wave amplitude changes107. If the P-wave amplitude is higher than the average of the mostprevious three P-wave amplitudes, then that indicates that the P-wave isincrementing, and the user is told to advance the PICC forward 108. A“local maximum P-wave” value is calculated and saved in memory as theaverage of the last three P-waves, and the algorithm loops back todetermine again whether or not the current P-wave amplitude is higherthan the average of the most previous three P-wave amplitudes. The usercommand to advance will typically be repeated for multiple cycles, asthe IV electrode approaches the SA node. Alternatively, if a currentP-wave amplitude is lower than the average of the most previous threeP-wave amplitudes, a further decision is made as to whether or not theamplitude of the P-wave is 60% lower than the average of the last threeP-waves, and whether or not the amplitude of the P-wave is higher thanthe P-wave threshold 109. The 60% threshold is for determining if thedrop in the P-wave was significant, indicating that the SA node may havebeen passed. However, a second check against the P-wave threshold valueis to ensure that the drop in the P-wave is at the very least above theP-wave threshold amplitude recorded when the IV electrode was positionedmuch further away from the SA node at the beginning of the procedure. Amore dramatic drop in the P-wave amplitude may otherwise indicate anissue, such as a signal acquisition error or a problem with thepatient's physiological activity. If both the amplitude of the P-wave is60% lower than the average of the last three P-waves and higher than theP-wave threshold, the algorithm determines that the absolute maximumP-wave has been reached. The most recent “local maximum P-wave” valuebecomes the “absolute maximum P-wave” value, and is saved in memory 110.At this point, user feedback instructs the user to move the PICC linebackwards 111, and the amplitude of the P-wave is measured and theaverage amplitude of the three most recent P-waves are calculated 112.

The next series of steps determines user feedback for moving the PICCline and IV electrode backwards to the target site. First, the algorithminstructs the user to pull back the PICC line until the averaged P-waveamplitude is within a particular range of the “local maximum P-wave”amplitude 113. An incrementing P-wave is now being tracked. When theP-wave amplitude is within range, the user is instructed to continue tomove the PICC line backwards 114. The amplitude of the P-wave continuesto be measured and the average amplitude of the three most recentP-waves is calculated 115. A decreasing P-wave amplitude is now tracked,and a decision is made regarding whether or not the average amplitudeenters the range of 75%-85% of the “absolute maximum P-wave” 116. Thecurrent range is indicated by the center bar on a level indicator GUI117. If the average amplitude is within the 75%-85% range, the user isnotified that the PICC tip is at the target location 118. If not, thealgorithm loops back to tracking the decrease in averaged P-waveamplitude. If the user pulls back too far, the algorithm canautomatically loop back to an earlier advance state, or a restartfeature can return the algorithm back to the beginning. In addition, thesystem can be modified so that the center bar reflects particular rangesthat correspond with the type of procedure being performed or the typeof catheter being placed. So for example, if the target location for thecatheter tip is further up the SVC, the center bar may be set to a65-75% range. Alternatively, if the target location for the catheter tipis further down into the RA, the algorithm can be modified so that theuser is instructed to stop once the decrementing P-wave amplitudereaches a particular range after hitting the maximum P-wave.

Now with reference to FIGS. 8A-8D, examples of GUIs 140, 141 for userfeedback are shown. Graphical instructions such as arrows, words,colors, or other symbols indicating advance PICC 142 or pull back PICC146 could signal an instruction to the user. Alternatively orconcurrently, audio commands can be utilized. The GUI 140, 141 could bepart of a touch screen handheld device, such as a smart phone or atablet. A GUI showing level indicators 144 can also be included.Waveforms of the surface ECG and IV ECG signals can also run on thescreen so that the user can monitor the resolution of the signal and theECG status of the patient.

In certain embodiments, a tip location procedure record is generatedafter each procedure for the patient's record. The tip locationprocedure record could record information including: (1) patientbackground information, including name, date of birth, a patient IDnumber, a catheter description, a user ID and miscellaneous notes; (2) agraphical display of ECG waveforms time stamped at various decisionpoints, such as verification of an acceptable surface ECG waveforms,advance ECG waveforms, pull back ECG waveforms, and a stop at target ECGwaveforms; and (3) a post procedure questionnaire assessing theprocedure, the patient, and any other relevant factors. The record couldbe saved electronically, printed out, or sent transmitted wirelessly toa local or remote server or database.

As mentioned above, tip location systems often use a stylet to trackchanges in the P-wave as the stylet advances towards the SA node. Thestylet may be similar to a conventional guidewire, or it could be aspecialty stylet with a plurality of electrodes, such as bipolarelectrodes disposed at different locations along the stylet. As shown inprior art FIG. 9A, the distal tip of a catheter 160 can have a stylet162 positioned at or near the distal opening for acquiring an IV ECGsignal. The stylet 162 acts as an electrode and transmits thephysiological ECG signal propogated from the SA node from the cathetertip to a proximal connection element such as an alligator clip. Thealligator clip is operably connected to the tip location system forsignal processing and interpretation of the IV ECG signal.

The invention claimed is:
 1. A method for establishing an ECG searchwindow for a catheter tip placement system, the method comprising:acquiring a plurality of ECG signals from at least one surface ECGelectrode, the at least one surface ECG electrode being connected to acentral processing unit (CPU), the CPU having a signal processing unit;generating a signal averaged ECG signal from the plurality of surfaceECG signals; determining a first fiducial point by identifying anextremum within the signal averaged surface ECG signal; establishing afirst ECG search window between first and second predetermined valuesoffset from the first fiducial point; determining a second fiducialpoint by identifying an extremum in the first ECG search window;determining a search window beginning value by identifying a localextremum on a first side of the second fiducial point, and determining asearch window ending value by identifying a local extremum on a secondside of the second fiducial point; and establishing a second ECG searchwindow between the search window beginning value and the search windowending value so that the second ECG search window is narrower than thefirst ECG search window; acquiring an intravascular ECG signal from anintravascular ECG electrode near the catheter tip, the intravascular ECGelectrode being connected to the central processing unit (CPU), the CPUhaving a signal processing unit; applying the second ECG search windowto the intravascular ECG signal to generate an intravascular ECG searchwindow; wherein the extremum in the signal averaged surface ECG signalis an extremum of an R-wave; and displaying signal data on a display,the display communicating with the CPU.
 2. The method of claim 1,wherein the first predetermined value is 40 ms prior to the firstfiducial point, and the second predetermined value is 220 ms prior tothe first fiducial point.
 3. The method of claim 1, wherein theplurality of ECG signals is measured over up to 15 heartbeats.
 4. Themethod of claim 1, wherein the local extremum on the first side of thesecond fiducial point is a first occurrence of a local extremum left ofthe second fiducial point, and wherein the local extremum on the secondside of the second fiducial point is a first occurrence of a localextremum right of the second fiducial point.
 5. The method of claim 1,wherein the step of acquiring a plurality of ECG signals from at leastone surface ECG electrode further comprises acquiring a plurality of ECGsignals from a plurality of surface ECG electrodes.
 6. The method ofclaim 5, wherein the plurality of ECG electrodes is three surface ECGelectrodes and the ECG signal is a surface signal.
 7. The method ofclaim 6, wherein the local extremum on the first side of the secondfiducial point and the local extremum on the second side of the secondfiducial point is determined using an algorithm test.
 8. A method forestablishing an ECG search window for a catheter tip placement system,the method comprising: acquiring a plurality of ECG signals from atleast one surface ECG electrode, the at least one surface ECG electrodebeing connected to a central processing unit (CPU), the CPU having asignal processing unit; generating a signal averaged ECG signal from theplurality of ECG signals; determining a first fiducial point byidentifying an extremum within the signal averaged ECG signal;establishing a first ECG search window between first and secondpredetermined values offset from the first fiducial point; determining asecond fiducial point by identifying an extremum in the first ECG searchwindow; determining a search window beginning value by identifying alocal extremum on a first side of the second fiducial point, anddetermining a search window ending value by identifying a local extremumon a second side of the second fiducial point; and establishing a secondECG search window between the search window beginning value and thesearch window ending value so that the second ECG search window isnarrower than the first ECG search window; acquiring an intravascularECG signal from an intravascular ECG electrode near the catheter tip,the intravascular ECG electrode being connected to the centralprocessing unit (CPU), the CPU having a signal processing unit; applyingthe second ECG search window to the intravascular ECG signal to generatean intravascular ECG search window; wherein the extremum in the firstECG search window is an extremum of a P-wave; and displaying signal dataon a display, the display communicating with the CPU.
 9. The method ofclaim 8, wherein the extremum in the signal averaged ECG signal is anextremum of an R-wave.
 10. The method of claim 8, wherein the firstpredetermined value is 40 ms prior to the first fiducial point, and thesecond predetermined value is 220 ms prior to the first fiducial point.11. The method of claim 8, wherein the plurality of ECG signals ismeasured up to 15 heartbeats.
 12. The method of claim 8, wherein thelocal extremum on the first side of the second fiducial point is a firstoccurrence of a local extremum left of the second fiducial point, andwherein the local extremum on the second side of the second fiducialpoint is a first occurrence of a local extremum right of the secondfiducial point.
 13. The method of claim 8, wherein the step of acquiringa plurality of ECG signals from at least one surface ECG electrodefurther comprises acquiring a plurality of ECG signals from a pluralityof surface ECG electrodes.
 14. The method of claim 13, wherein theplurality of surface ECG electrodes is three surface ECG electrodes andthe plurality of ECG signals are surface signals.
 15. The method ofclaim 8, wherein the local extremum on the first side of the secondfiducial point and the local extremum on the second side of the secondfiducial point is determined using an algorithm test.